The present invention relates to an apparatus for detecting bonding defects of a semiconductor element such as an IC by monitoring an output waveform of an ultrasonic oscillator of a bonder.
In the case of a semiconductor element having as many as several hundreds of pins, it is usual to determine the quality of the products by bonding the pins using ultrasonic waves and then measuring the characteristic of the product with a semiconductor tester. However, with this method, even when bonding strength does not satisfy rated value, if the pins are only electrically connected, no bonding defect will be detected, and there is a high possibility that several bonding defects may appear after the product has been shipped.
Further, although there is conventionally a bonding defect detecting apparatus aiming at the variations of voltage waveform and current waveform of an ultrasonic oscillator of a bonder, the measuring method is based on the measurement of absolute values. That is, the apparatus is used to measure the effective values of the voltage and current during the bonding operation, setting a reference value based on the average value thereof, and determining whether or not the product is qualified by setting this reference value to be a fixed value.
However, in the case of an actual bonding for an IC, there are differences in reference values resulting from different types of apparatuses or semiconductor elements, or there are differences in average value due to positions of the pins on the frame. Therefore, using the reference value as a fixed value is not practical because of gross errors produced when determination is made.
Further, even in the case of the same semiconductor element, effective values of voltage and current fluctuate with time due to wear, and a rise in temperature, of the tool at a top end of the bonder, and the conventional apparatus using average values has a problem of being unable to cope with the fluctuation, with the result that the criterion of determination of the quality of the product is not kept constant.